Various non-collagenous, non-proteoglycan proteins have been described in articular and non-articular cartilage. The function of most of these proteins is unknown. We have recently identified a high molecular weight (greater than 400,000-dalton) protein, with 116,000-dalton subunits, in all normal articular cartilage studied, as well as in normal bovine tracheal cartilage, atrophic canine knee cartilage, and osteoarthritic human hip cartilage. This protein constitutes approximately 3-7% of the total non-collagenous protein in 4 M guanidinium chloride extracts of normal articular cartilage and is one of the major non-collagenous proteins synthesized in 24-hours organ cultures of normal canine knee cartilage. Immunofluorescence studies using specific antiserum reveal that the 116,000-dalton protein is found in the interterritorial and pericellular regions of normal adult and fetal cartilage. Only a small amount of cross-reacting material is present in menisci, synovium, and synovial cell cultures. This protein is not present in serum or synovial fluid, which provides evidence that it is not adsorbed from these sources onto cartilage. The goals of the studies proposed in this application are to purify the greater than 400,000-dalton protein from articular cartilage of immature, mature, and osteoarthritic dogs; to explore its interactions with collagen, proteoglycans, and hyaluronic acid; to quantitate it in the various cartilages; and to study its biochemical composition and metabolism. This project will thus contribute new information concerning what appears to be a major non-collagenous protein of normal articular cartilage. It may also enlarge our understanding of the macromolecular composition of cartilage in aging and ostearthritis.